1. Field of the Invention
The invention relates generally to optical communications, and more specifically to a variable attenuator for removing optical energy from a waveguide in a controllable manner.
2. Description of the Prior Art
The telecommunication industry is making increasing use of optical communication systems for high-bandwidth transmission of voice, video, and data signals. In optical communication systems, it is frequently necessary or desirable to precisely adjust optical signal levels entering various system components. Adjustment of optical signal levels is typically achieved by incorporating variable optical attenuators into the optical circuits. In one example, a variable optical attenuator may be employed to equalize power levels among separate channels of optical circuits implementing wavelength division multiplexing (WDM). Variable optical attenuators may also be employed to avoid exposing optical detectors to excessive signal levels, which may damage the detectors and cause them to become inoperative.
Various references in the prior art disclose attenuators for use in optical circuits. Examples of such attenuators include those described in U.S. Pat. No. 4,762,383 to Yamashita et al. (“Two Dimensional Light Beam Deflectors Utilizing Thermooptical Effect and Method of Using Same”); U.S. Pat. No. 5,881,199 to Li (“Optical Branching Device Integrated with Tunable Attenuators for System Gain/Loss Equalization”), and; U.S. Pat. No. 5,966,493 to Wagoner et al. (“Fiber Optic Attenuators and Attenuation Systems”). The attenuators described in the foregoing references, as well as other prior art attenuators, are known to suffer from operationally significant problems or limitations. These problems include sensitivity to ambient temperature, high power consumption, limited or no adjustability, the occurrence of cross-talk between adjacent channels, high coupling losses, bulkiness and slow responsiveness. Further, some prior art attenuators have moving parts that tend to degrade over time and have associated mechanical resonance.
Thus, there is a need in the optical communications art for a variable optical attenuator which overcomes the problems associated with prior art devices.